This invention relates to improved lubricating oil compositions. More particularly, this invention relates to lubricating oil compositions which include solid materials to enhance the properties of such compositions.
Oil compositions are conventionally used to lubricate internal combustion engines, for example, such engines which power motor vehicles. Previous studies have indicated that the inclusion of certain solid materials, e.g., graphite, in these oil compositions improves the engine's fuel efficiency. For example, studies reported in "Stable Colloid Additives for Engine Oils -- Potential Improvement in Fuel Economy", James E. Bennington et al, Society of Automotive Engineers, Fuels and Lubricants Meeting, Houston, Tex., June 3-5, 1975, indicate that a gasoline mileage improvement of between 3 to 5 percent is obtained by adding one percent graphite to a conventional lubricating oil composition. Such improvement in fuel economy is particularly valuable in view of, for example, the short supply of such fuels.
However, other criteria must be met by lubricating oil compositions in order to be effective in modern internal combustion engines. For example, such compositions are required to meet certain specifications with regard to tendency to form deposits, e.g., varnish, sludge and the like, on engine components. The presence of the solid lubricants in these compositions tends to increase these deposit forming tendencies.
A lubricating oil composition containing at least one of certain solid lubricants and having acceptable deposit forming characteristics is clearly desirable.
Therefore, one object of the present invention is to provide an improved lubricating oil composition.
Another object of this invention is to provide a solid particle-containing lubricating oil composition having reduced deposit forming tendency.
A still further object of the invention is to provide an improved method of lubricating an internal combustion engine. Other objects and advantages of the present invention will become apparent hereinafter.